A printing method identifies where parts of an image will not be printed correctly due to partial or total device failure and if possible adjusts the size of ink dots in adjacent rows or columns so as to lessen the visual effect of failure to print at the original location.
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1. A method of modifying an image to be digitally printed by a printing device to compensate for failure to correctly print dots of ink at specific locations, the method including the steps of:
identifying a first defective location,
identifying a second location adjacent or near to the defective location;
compensating for the defective location by adjusting the dot size of the second location; wherein
the step of adjusting the dot size of the second location occurs without adjusting the dot size of the defective location.
7. A printer having a row of activatable devices which, when activated, cause rows of dots to be deposited onto a substrate and means to move the substrate relative to the row of devices in a direction generally perpendicular to the row of dots, said printer including:
analyzing apparatus to determine if one or more of said devices is not operating correctly; and
control means for analysing images or image data and for identifying a first defective location where a dot of ink should be printed by activation of an incorrectly operating device and to determine a second location adjacent or near to the defective location; and
compensating means to compensate for the defective location by adjusting the dot size of the second location; wherein
the compensating means adjusts the dot size of the second location occurs without adjusting the dot size of the defective location.
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This invention relates to digital printing and more particularly to printing using devices which eject ink onto the printed substrate. However, the invention is not limited to ink ejection devices and is also applicable to laser, light emitting diode printers and to digital photocopiers.
In ink ejection devices a printhead has an array of nozzles through which ink is selectively ejected onto the substrate as the substrate moves relative to the printhead. The printhead may print by scanning across the substrate to print horizontal bands or, if it is a full page width printhead, it may pass along the length of the page. A blocked nozzle will result in multiple horizontal blank lines, in the case of a scanning type printhead, or a blank vertical line in the case of a page width printhead. Such blank lines are undesirable since they detract from the printed result.
The present invention provides a method of modifying the printing of an image so as to reduce or effectively eliminate the visual effect of one or more such blocked nozzles apparent to the eye of an observer in normal use. However, the invention is applicable to other forms of printing where a device, whether passive or active, is repeatedly used to produce dots of ink or the like on a substrate. The invention has potential application to laser and LED type printers and photocopiers where a fault in the imaging drum or light source can result in repeated faults in the image produced. As used above and throughout the description and claims the term image is to be understood to have a broad meaning and includes anything printed, such as text and line drawings.
In one broad form the invention provides a method of modifying an image to be digitally printed by a printing device to compensate for failure to correctly print dots of ink at specific locations, the method including the steps of:
In another broad form the invention provides a printer having a row of activatable devices which, when activated, cause rows of dots to be deposited onto a substrate and means to move the substrate relative to the row of devices in a direction generally perpendicular to the row of dots, said printer including:
The incorrectly operating device will result in a defect line or lines in the image printed. Usually the incorrectly operating device will produce no ink or not enough ink and so a blank or faint line will be produced. To compensate adjacent ink dots will be caused to be larger than required by the raw image data. Conversely if the incorrectly operating device is producing oversized ink dots, the dot size of adjacent dots will be reduced.
Where a part of an image requires the incorrectly operating device to deposit a continuous or substantially continuous column of dots, the dots in adjacent columns are preferably all adjusted in size. If there are a small minority of locations in the column of the incorrectly operating device which do not require ink, dots in adjacent columns may or may not be adjusted in size.
Dots in more than the two adjacent columns may be adjusted in size. Dots in adjacent columns may be adjusted in size only if they are within predetermined vertical or horizontal distances or both of one or more specific location. For example only dots in the columns either side of the failed column may be adjusted in size but dots in those columns two or three rows above and/or below the respective location may be adjusted in size.
The invention shall be better understood from the following non-limiting description of preferred embodiments and the drawings, in which
Referring to
For the purposes of explanation it is assumed that inkjets a-g and i-n inclusive are operating correctly but, for whatever reason, inkjet h is not operating correctly or at all. It is also assumed that the diagnostic systems of the printer, which will be well understood by those skilled in the art, have detected that nozzle h is not functioning correctly. In most cases, a malfunctioning device will be partially or totally blocked resulting in insufficient or no ink being deposited on the paper.
Referring to
Referring to
In the
The area of each adjusted size dot is preferably increased by about 50% but this may be more or less, as needed. The oversize dots in the two columns may just touch dots in the same column. However, the size increase may be less, such that the dots in each of the two columns of dots do not join, or may be greater, such that adjacent dots overlap.
Where ink dots are required in column h at frequent intervals oversize drops will be deposited continuously by nozzles g and i. It will be appreciated that when ink dots are deposited less frequently the drop size of ink in columns g and i will only increase adjacent or near to areas where drops should occur in column h. These moversize drops may extend into rows where no ink is intended in column h. Where ink is not intended in column h for large distances, preferably no oversize drops will be created in columns g and i.
Referring to
In the case of ink ejection type printers, increased dot size is achieved by increasing the amount of ink ejected. In the case of thermal ink ejection devices this may be achieved by increasing the duration of the heating current pulse. In the case of piezo electric ink ejection devices this may be by increasing the driving voltage or current to cause greater distortion or by increasing the pulse duration. Similarly with mechanical type ink ejection devices the pulse width and/or driving voltage or current may be increased.
The invention is also applicable to situations where individual devices are producing too much ink, in which case the adjacent devices may be adjusted to reduce the dot size of ink dots produced.
It will also be appreciated that this technique may be used with laser and LED printers and photocopiers and other types of digital printers where the placement of an ink dot is dependent on individual activation of a device or component. For example, an LED in a LED printer may fail or there may be a defect in the photoconductive imaging drum of a laser printer. In both cases, adjusting the size of adjacent dots can hide or reduce the visual effect of the defect in the device or component.
In the case of a laser or light emitting device type printer dot size may be modified by modulating the intensity and or total amount of the light falling on the corresponding portion of the photoelectric imaging drum.
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